Electric furnace.



' H. AQGREAvEswsL H. ETCHELLS.

ELECTRIC FURNACE.

APPLICATION FILED MAR. 1. |911.

1,257,9'97. Patented Mar. 5, 1918.

HENRY ARNOLD GEAVES AND HARRY ETCHELLS, OF SEFFIELD, EN

ELECTRIC FURNACE.

lpecicatlon of'Letters Patent.

Patented Mar. 5, 1918.

Application med-larch 1, 1917. Serial No. 151,635.

To all whom z't may concern.'

Be it known that we, HENRY ARNOLD GREAvEs and HARRY E'rcHELLs, B. Met., subjects of England, residing at Raven road, Sheffield, and 231 Oakbrookk road, Sheffield, 1n the county of York, respectively, haveinvented new and useful Improvements in Electric Furnaces, of which the following 1 s a specification. l

Our invention relates to a method of distributing two phase and three phase currents to electric arc furnaces and resistance furnaces, and consists in effectin the distribution in such a manner that t e supply phases tend to have balanced loads.

Our invention will be better understood on reference to the accompanying drawings in Which l Figure 1 shows our invention asl applied y' to a' three phase supply system, and

Fig. 1 1s a diagrammatic sketch of the arrangement of primary windings.

Fig. 2 shows our invention as applied to avtwo phase supply system. The same letters refer to similar parts throughout the several views.

furnace as shown in Fig. lhaving two top electrodes or e and a conducting hearth or bottom electrode, c, is connected with the low tension terminals of three single phase transformer windings OA, OB, OC which are grouped in star fashion so that one low tension kterminal of each transformer is connected to the star point O, and the other low tension terninal to the respective electrodes, a, b, all C. i

The primary windings of this transformer System are grouped in delta or mesh connection as shown in Fig. 1.

The two transformers OA, OB are identical in ower and transforming ratio, `but the secon ary voltage OC must be less than OA or OB. The exact voltage OC varies according to the resistance of the bottom electrode c.

By means of an auto transformer, or taplpings incorporated in the secondary windings vof' the transformer OC or the corresponding lprimary winding, the secondary voltage can be varied until the loads on the primary s u ply phases are exactly balanced, assuming t at the currents through electrodes a and b are equal.

By varying the voltage OC the amount groups'of electrodes, a, b,

i oaded, when the electrodes is such that equal currents pass lseparate phase of a two of current taken by the electrode c, can be varled, with only a slight displacement of the balance of the primary phases. This re-v sults ina passage of more or -less current between the electrodes a, b.

In Fig. 2 is shown an arrangement of transformers whereby two phase currents may be supplied to. such a .furnace of the type herein referred to, -in such a manner that one top electrode cannot be moved Without affecting both phases of the supply system. From this ligure it will be seen thatthe two top electrodes aand b are each connected to the opposite ends of the low tension windin of a transformer AB supplied by one pase of a two phase supply. One terminal of the low ltension winding of another transformer D is connected to the middle point O of the low tension winding of the transformer AB; the other terminal connected tothe furnace bottom or This last named bein a to t e lower electrode c.

transformer is separately excited by the other phase of the two phase. supply system.

If the first mentioned transformer AB has a secondary voltage between its terminals which is twice the secondary volta e between the terminals 0f the transformer T), the two phases of primary supply will be equally adjustment of the two top throu h each electrode. The secondary .voltage 0 the transformer AB may be less than twice the secondary voltage between the terminals. of the other transformer D, when resistance is interposed in the bottom electrode, but is always greater than the secondary voltage of said other transformer.

From the foregoing it will be seen that our improved arrangement is substantially different from the two phase arrangements usually employed wherein two equal single phase transformers are each connected to a hase supply, thus enablin one phase to be oaded many more times t an the other without the one phase affectin the load on the other phase.

It wil also be seen that in the beforegoing described methods of arranging transformers, no short circuiting can occur between either ofthe top electrodes and the bottom,

without the ensuing rush of'current having to traverse two transformers in series. This has a considerable damping or'choking effect loo in the extent of the current overload, and

minimizes the extent of sudden overloads on the supply system which constitute a serious drawback to most other types of furnace.

Having now described our invention what we claim as new and desire to secure by Letters Patent is:

l. In electric arc or resistance furnaces having upper and lower electrodes, the improved method of distributing three phase currents so that the supply phases have balanced loads, consisting in the arrangement of three single phase transformers grouped in star fashion, and having the primary windings grouped in delta or mesh connection, so that the two transformers connected to the two upper electrodes or groups of electrodes are identical in power and transforming ratio, while the voltage of the transformer connected to the lower electrode is less than either of the other two, the exact voltage varying accordin to the resistance of the lower electrode in t e manner and for the purposes substantially as herein described and illustrated.

2. In electric arc or resistance furnaces having upper and lower electrodes varying the secondary voltage in the transformer connected to the lower electrode by means of an auto-transformer or primary tappings incorporated in said transformer, whereby the loads on the meshed primary supply phases are exactly balanced, when the currents through the uppergelectrodes are equal, in the manner and for the purposes substantially as herein described.

3. In electric arc or resistance furnaces having upper and lower electrodes the improved method of distributing two phase currents so that both supply phases are always loaded when either electrode carries current, consisting in connecting the two upper electrodes or groups of electrodes to the opposite ends of the low tension winding of a transformer supplied by one phase of a two phase supply, and connecting the lower electrode to one terminal of the low tension winding of another transformer excited by the other phase of the two phase supply system and which has its other terminal connected to the middle point of the low tension winding of the first named transformer, in the manner and for the purposes substantially as herein described.

4. In electric arc or resistance furnaces having upper and lower electrodes the arrangement of the transformer `connected with the upper electrodes, with a secondary voltage between its terminals which is twice or less than twice (if resistance be interposed in the lower electrode) the secondary voltage between the terminals of the other transformer, but always greater than the secondary voltage in said other transformer whereby the two phases of primary supply are equally loaded when equal l currents pass through each of the upper electrodes, in the manner and for the purposes substantially as herein described.

5. In electric arc or resistance furnaces having upper and lower electrodes, worked by two phase or three phase currents, the improved arrangcment and grouping of transformers whereby the supply phases always 4.tend to have balanced loads, substantially [as herein described and illustrated on the ac-V companying sheet of drawings.

6. An electric arc or resistance furnace having upper and lower electrodes wherein considerable resistance can be introduced through the bottom electrode without mingling phases and impairing the power factor of the system, substantially as herein described and illustrated.

7. The method of distributing alternating current to an arc or resistance furnace having upper and lower electrodes, which consists in connecting the secondary circuits of a-transformer system to the electrodes of the furnace, the secondary windings of the transformer system being such that the load on the primary supply phases is balanced.

8. The method of distributing alternating current to an arc or resistance furnace having upper and lower electrodes, which consists in connecting the secondary circuits of a transformer system to the electrodes of the furnace, and regulating the voltage of one of the secondary windings of the transformer system to balance the load on the primary supply phases thereof.

9. The combination of an electric furnace having upper and lower electrodes, a transformer system having current generated in its secondary windings, one or more of the secondary windings having a lower voltage than the others, and connections between terminals of the secondary windings and the respective electrodes.

In testimony whereof we have signed our names to this specification in the presence of two subscribing witnesses.

HENRY ARNOLD GREAVES. HARRY ETCHELLS.

Witnesses:

R. HEBER RADFORD, F. WALKER. 

